Truck bucking like a bronco

[FiveFlat]

Specs:
'05 F-350 crewcab dually. 2WD, auto trans, 6.0L, 3.73 rear end. Hypertech PTM in-line module. Exhaust dumps to ground right behind Cat.

The hypertech is the in-line system with the 3 stages to it. They advertise that it is fully tow capable at level 3. I haul a 5000-10000lbs gooseneck horse trailer or sometimes a flatbed trailer for tractors, etc.
When I get right at 59mph, it starts bucking like crazy. I have to let completely off the accelerator and coast down to around 55, or floor it and get up to around 64mph. I tried turned the PTM down to level 1 and sometimes level 0 (stock) and that seemed to alleviate the problem. But it's getting worse. Now it's doing it without a trailer at all levels other than 0.
Obviously, I'm pointing my finger at the Hypertech PTM, but has anyone else experienced this?

[KYStrokin]

I have an 04PSD with an sct tuner and mine does the exact same thing. I wish i knew what was wrong.